High-frequency strap-wound coils



lNVl-ZNTOR WILLIAM F. SANDS 87/ ATTORNEY W. F. SANDS HIGH-FREQUENCY STRAP-WOUND COILS Flled May 2'7 1948 March 6, 1951 Patented Mar. 6, 1951 Price man-resonator s'rnar-wousn cons William F. sum, Haddoniield, N. 1..

Corporation of ware 'Radlo .ofDeia alsignor to a corporation Application May 27. ms, Serial No. 20,028

This invention relates to high frequency inductance elements, and particularly to. coils wound with a single layer of wire or a fiat strap of conducting material which are to be tuned through an extended frequency range by a movable core. This application is related to a portion of my copending application filed on June 28, 1943, Serial No. 492,506, and entitled "Permeability Tuning System, now Patent No. 2,486,986.

An inductance element for use in high fre- 2 and being arranged to form a dense current sheet. Such coils were not available heretofore.

It is the principal object of the present invention, therefore, to provide novel strap-wound inquency resonant circuits must be made with a comparatively small inductance. A high frequency inductance coil accordingly usually consists of a few turns of a conductor such asa wire.

It is frequently desired to high frequency range by moving a core relatively to the inductance coil of the circuit. In that case, the coil is usually wound with a few turns of wire which are spaced very widely. Accordnslv. the intensity of the magnetic fielddevelopedwhen' current flows through such a coil is not uniform along the length of the coil. However, in order to vary the inductance of'a high frequency coil in a continuous manner by a movable core, a magnetic field is very desirable which is substantially continuous, that is, it doesnot have appreciable discontinuities.

tune a circuit over a Inductance elements are known which consist.

of a strap of conducting materialvfiat-wound in the shape of a helix. Such an inductance element may have a comparatively uniform .current sheet.

A current sheet is defined by F. W. Grover. in his book "Inductance Calculations" publishedin 1946 by D. Van Nostrand Co., Inc., New York, for example, on pages 15 and 142, as a winding where the current flows around the in a very thin layer on the surface of the cylinder.

- Such previously known strap-wound c0ils, however, did not have closed end turns. that is, the free end of the coil strap extends for the width of thevstrap beyond the last turn. It is obvious that only that portion of the coil may. be used for tuning it which has a uniform current sheet and that excludes the end Portion of the coil. Movement of a corev within the end portiom of the coil will not vary its inductance'as effectively.

axis of a cylinder ductance elements suitable particularly for use in high frequency tunable resonant circuits, and straps of conducting material for such elements.

Another object of the invention is to provide novel, high frequency coils wound with a strap or with a single layer of wire forming part of a resonant circuit, and which may be tuned by a movable core through a larger frequency range than was possible heretofore. I

A further object of the invention is to provide strap-wound coils with uniform or non-uniform pitch which may be used in a superheterodyne radio receiver for the purpose of providing a constant frequency difference between the continuously variable resonant frequencies of two resonant circuits, the circuits being tuned by moving a core relatively to an associated strap-wound coil.

Still another object of the invention is to provide, in a superheterodyne radio receiver, an improved variable tuning system having movable cores for causing the oscillator and signal input circuits to track accurately one with the other at a multiplicity of points throughout a predetermined frequency range.

In accordance with the present invention, there is provided a high frequency inductance element consisting of a strap of conducting material arranged in helical shape and having closed'end turns extendingbetween two spaced planes arranged at right angles to the longitudinal 'axis of the element. In this manner it is possible to form a uniform dense current sheet extending between the, two planes. The inductance element as a corresponding movement of the core in the" center of the coil. Consequently, fora given length of coil, the frequen y. t ough which it can be tuned is. diminished by the ex'istence'of a discontinuity of the current's'heet. Thus, the

previously known stra'p' wound coils can not be: tuned by a movable coreovei' the wide tuning' range frequency required. In some inductanceeoilsareneeded,havinga'variablepitch or coil may be wound as a helix having a uniform pitch, or having a non-uniform pitch, such as a helix with a uniformly varying pitch. Thus, the coil may consist of a winding of uniform thickness and variable width.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The operation itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in con'-' nection with the accompanying drawing, in

which:

Fig.1 is a view in perspective of an inductance element wound in the shape of a helix with uniform pitch and embodying the present invention;

- dotted lines.

Fig. 2 is a developed view of the strap of which the inductance element of Fig. 1 is formed;

Fi 3 is a view in perspectiveof a modified inductance coil in accordance with the invention. having a unifcrmiyvarying pitch;

Fig.4isagraphillustratingthemannerm which the strap of which the coil of Fig. 8 cmsists may be designed;

Fig. 5 is a view in perspective of another embodiment of the invention, consisting of a helically wound coil with uniformly varying bitch and closed end turns;

Fig. 6 is a developed view of the strap of the coil of Fig. 5;

- Pig. '7 illustrates a modified inductance coil in accordance with the present invention;

Fig.8isaviewinperspectiveofaninductance coilconsisting ofatrifilanabiiilarandasingis wire section to provide windings of va yi width;

and

Fig.9isacircuit'diagramcfaportioncfa superheterodyne receiver including a pre-timer and frequency converter wherein the inductance elements of Figs. 1 and 5 may be used.

Referring now to the drawing, and particularly to Figs. 1 and 2, there is illustrated a strap-wound soil III, which may be wound on a coil form II of suitable insulating material such as Bakelite. Coil form I l preferably is in the shape of a cylinder, as illustrated. Coil it may of course be made self-supporting in which case coil form I i may be omitted.

Coil It consists of a strap or sheet of conducting material such as copper or silver. and is wound in helical shape and provided with two right cylindrical end turns illustrated at I! and i8. Coil form ll need not necessarily be of sir-- cular cross-section, but may have instead a square or rectangular cross-section. In that case a helical coil II is obtained having a non-circular crosssectlon. Coil II is wound with a uniform pitch, and a suitable gap is provided between adjacent turnssoasnottoshort-circuitthecf the coil. Alternatively, the conducting strap obtained may be suitably insulated. for example, by covering the strap with lacquer, and in that case the strap may be wound without a gap.

The strap of which inductance coil II is formed isshapedasillustratcdinl 'igd andconsistsof a main portion II and two end portions i0 and I1. Themainportion ithastwoflaredparaliel edges i and I forming an angle a with the vertical edge I of end portion it, where a is the pitch angle of the coil. End portions i0 and II are of triangular shape having their apices adjacent to straight horizontal edges i8 and 20 of the strap. End portions i8, i1 have vertical edges 3, l and horizontal edges 8, 6. The length of vertical edge 3 or 4 is determined by the circumference of coil form H, which is the circumference of the coil.

The width of straight edges and II, which is the width of main portion I i, is determined by the distance between the centers of two adjacent windings or turns of coil ill. The total distance between straightedges I8 and is given by the desired number of turns of the coil and the cell diameter. The strap illustrated in Fig. 2 may be wound into a coil having four complete turns. for example, so that the distance between edges ll and 20 does not exceed 4.1!. as illustrated.

The strap of Fig. 2 may also be considered as consisting of a main portion bounded by straight edges l, 2 and by vertical edges 1 and 8 shownin In that case," end portions I and 4 straightedges ltJJandlandbyedgesi..." and 4. respectively.

When coil II is wound with an insulating gap between the individual windings as illustrated in rig. Litwiilbenecessarytoremove asmallstrip fromthestrapcfl'ig.2alongedgesil, i andl. Alternatively, a small strip may be removed along edges I. I and II. The portion removed from thestrapshouidcorrespondtothe desiredwidth of the insulating 8w of coil ll.

Strap-wound coil ll accordingly permits the formation of a uniform dense current sheet betweenthetwoplanesbetweenwhichtheeoll extendsi This means that the current flowing through'coil ilisofsubstantially uniform density betw'eenthetwcpianesandtherebyproducesa uniform magnetic held. In view of its closed end turns. inductance coil ll maybe tunedby amovabieccreoveralargerfrequencyrangeinamanner to be presently explained. The coil preferablyisusedinthehighfrequency rangebetween approximately 30 and 300 megacycles.

Inductance coil it may with its inherent distributed capacitance, or a connected shunt condenser form a resonant circuit which may be tuned in various ways. Thus, it is feasible in move a paramagnetic core within coil form ii to effect permeability timing of the coil. A paramagnetic material is defined as a material having a magnetic permeability greater than that of a vacuum. which is unity. The magnetic permeability of a etic material may be independent of the magnetizing force or it may vary with the magnetizing force, in which case the material is usually called ferromagnetic.

It is furthermore feasible to tune the resonant circuit including inductance coil in by moving within coil form li a. core which may consist of a high conductivity non-magnetic metal such as copper, brass, aluminum or silver. In this manner eddy currenttuning of the coil in may be elected. Finally, it is feasible to move within coil form II a core which consists of a material having a high dielectric constant. Certain ceramic materials are suitable for this purpou.

such as barium. strontium or calcium titanates having a dielectric constant larger than 1000. In this manner the capacitance existing between thecoreandthewindingscfcoil llmaybevaried, thereby to provide dielectric tuning of the coil. These three types of tuning may generically be termed core tuning."

Itistobounderstoodthatcoil Ill neednotbe wound from the strap illustrated in Fig. 2, but the conductor may be applied to coil form II by electrolytically depositing a conducting material on the coil form or by spraying or printing the conducting material, or other well known methods. to obtain coil II. A method of obtaining a printed inductance has been disclosed by Ryder in Patent No. 1,837,678. By following the teachings of Schoop, 1,256,589, an inductor may be obtained by spraying metal on a coil form.

Referring now to Fig. 3, there is illustrated an inductance coil 28 consisting of a specially shaped strap of considerable tapered width and having flared end turns. The strap may therefore be wound in helical form with a uniformly varying pitch. Coil Il may be wound on a cylindrical coil form H. For some purposes it is desirable to have an inductance coil with a non-uniform pitch. Accilofthistypemaybeusedwith advantage for obtaining tracking in a superheterodyne receiver. If the coil is wound from H consist of rectangles which are boimded by 15 a strap of non-insulated conducting material, it

. is, of course. important that the strap be formed in such a manner that there is an insulating gap between successive windings or turns thereof.

Referring now to Fig. 4, a curve is illustrated which may be employed in determining the shape of strap 26' which may then be utilised for winding coil as. The outline of the edges of i strap 28 may be determined; by the formula Z=j(0), where !(0) isdetermined by the desired variation of the pitch angle. As shown in Fig.

4, Z is the ordinate and 0 the abscissa which equals theangle from the beginning of the winding of coil 25 to a given point on strap it as illustrated in H8. 8.

Let it beassumed that it is desired to wind coil 25 with a uniformly varying pitch, where the second derivative of {(0) becomes a constant. Accordingly, let

' was... which is the formula'of a parabola. l lor Z=zo and, accordingly,

Zo=c

In Fig. 4, c has been made equal to 0.

The value of the constants a and b may be determined in the following way:

and

I for a parabola.

The upper edge 21 of strap It is obtained by the formula while the lower edge 28 of strap is is obtained by the formula Thus, the upper edge 21 has the same curvature as the lower edge 28, but is displaced by 21, or a full winding, from that of the lower edge 20. Strap 26 is terminated by two straight edges 3.

and II which extend parallel to the Z=0 axis,

edge 30 coinciding with the 2:0 axis while edge 3| is spaced from edge 30 a distance corresponding to the desired number of turns of coil II,

which equals four in Fig. 4. The length of edges 30 and 3| is determined by the width of the first and last turns, respectively, of coil 2!. The abscissa distance 21 corresponds to the circumference of .the helix, that is, of coil 25.

It will be understood that strap It may also be developed according to the formula 2:10). In that case, Z=b0+c, which is the equation of a straight line, where b and e have the values given hereinbefore. Thus, b again equals tan a and, because the pitch is uniform, the angle a is the same for the entire strap.

It will be observed that cell 25 does not have closed end turns. It has already been pointed out that it is very desirable to provide a strap- -wires connected together at the mit the formation of a uniform dense current sheet. Such a coil is illustrated in Figs. 5 and 6. 0011 u mayagalnbewoundonacylindrical coil form II and the developed strap, shown in Pig. 6, may have a main portion It corresponding to the strap of Fig. 4. In order to provide the closed end turns, strap 20 is provided with two substantially triangular end portions 34 and II, each having an edge parallel to edges 30 and 8| and another edge extending at right angles thereto. The length of each triangle 34 and II is determined by the circumference of coil form ll, while the height or width of each triangular portion ,3! is determined-by the width of the windings at the beginning or end of coil 33.

Since coil 33 has a non-uniform pitch, that is,

to the 0=0 axis and a vertical edge which determines the height of triangular portions ll, 35 arranged parallel to the Z=0 axis.

It is to be understood that it is also feasible to wind a coil from a strap designed according to another function of 0, depending upon the. desired change of the pitch angle.

In Fig. 7 another possible coil structure is shown in which an auxiliary inductance L1 is .wound on coil form F over a portion of a tuning inductance Lo. Indeed,- it may be possible to wind the auxiliary coil Ll between the turns of the tapped portion of coil Lo, thus forming a biiilar portion on cell Lo. Coils Lo and Li may be tuned by movable core 0c.

The coil structure of Fig. 7 may be considered as consisting of a single layer winding of uniform thickness where successive turns are of diflerent effective widths. In other words, the bifllar portion of coils L: and Lo has the same eiIect as a strap of conducting material of the same width as the parallel wires. because adjacent points of the bifllar winding are equipotential.

It is also feasible to wind an inductance element consisting of a plurality of sections the conductor in each section having a different effective width with respect to the conductor of the other sections. Such a coil 38 is illustrated in Fig. 8 and consists of three sections 31, I8 and II which are wound upon coil form II. Section 31 consists of a trifllar winding, the three parallel wire conductors being connected together as illustrated at 31'. Section 88 consists of a bifllar winding with the two parallel and endof the Miller winding, as shown at It and it. Finally, section 39 consists oi'a single wire. Accordingly, the eil'ective width of the conductor forming coil 36 varies from section to section.

pitch as illustrated, or it may have a non-uniform pitch.

I advantage in Inductance coils Ill and 38 may be used with a superheterodyne receiver of the type illustrated in Fig. 9. Th circuit includes a dipole antenna ll for intercepting a high frequency-modulated canier wave which is impressed on a tuned input circuit 4|. Dipole antenna' III is connected across coil 42 which is inductively coupled to coil 43 across which is connected a condenser 44. Coil 48 may, for examguano and anode It. An automatic volume control voltage (AVC) may be impressed through resistor ll on signal control grid 41.

The oscillator section is coupled between cathode II and oscillator control grid Ii and comprises a tuned tank circuit I6. Tank circuit It includes coil [1, bypassed by two series condensers I8 and II. Coil I! may be identical with coil 33 of Fig. 5 and may have a uniformly varying pitch to secure tracking of tuned circuits 4| and It. The Junction point of coil 51 and condenser 10 is grounded as shown. The circuit may be tuned by core I, which may be moved in unison with core I! as indicated at 82 and which may consist of the same material as core 45; The junction point 01 condensers l8 and 60 is connected to cathode II, which is grounded through choke coil 08. The high potential terminal of tank circuit I is coupled to oscillator control grid ll through coupling condenser 04. Grid may be grounded through grid leak resistor 05.

The oscillator section is arranged as a Col itss oscillator and operates in a conventional manner. The screen grids II, It connected together to a suitable source of P itive voltage, indicated at +3, through dropping resistor 86. Screen grids II, 53 are bypassed for radio-frequency currents by grounded condenser 81. The intermediate frequency may be obtained from anode circuit II, connected through resistor Ii between +3 and anode SI, and the intermediate-frequency signal may be derived from output circuit 12, magnetically coupled to anode circuit II.

The operation of the circuit of Fig. 'l is conventional and no further explanation is needed here. For the purpose of obtaining tracking, a strap-wound coil with uniform pitch, such as coil Il, may be used in the radio-frequency input circuit I, while a strap-wound coil with uniformly varying pitch, such as coil 38 or coil I having a variable winding width, may be used in oscillator tank circuit 80.

There has thus been described a high frequency strap-wound coil of uniform pitch arranged in such a manner as to permit the formation of a uniform dense current sheet throughout the length of the coil. Furthermore, a strapwound coil has been disclosed which may have a non-uniform pitch, such as a uniformly varying pitch. This coil may take the form of a coil consisting of wire conductors of varying effective width. The strap-wound coil of non-uniform pitch may also be arranged in a manner to provide clom end turns. Two strap-wound coils, one having a uniform pitch and the other having a uniformly varying pitch may be used, for example, for securing tracking in a superheterodyne receiver.

What is claimed is:

1. A high frequency inductance element consisting of a strap of conducting material of considerable width along the entire length of the or substantially right cylindrical shape adjacent respectively to two spaced planes at right angles to the longitudinal axis of said element, thereby to permit the formation of a uniform dense current sheet between said planes.

2. A high frequency inductance element consisting of conducting material having considerable width and flared end pieces. said element being arranged helically with a uniform pitch in the shape of a cylinder having right cylindrical sections adjacent to two spaced planes arranged atright anglestothelongitudinalaxisofsaid element, thereby to permit the formation of a uniiorm dense current sheet between said planes.

3. A high frequency inductance element consisting of a strap of conducting material of considerable tapered width along the entire length of thestrap andhavingfiaredend pieces,'eaid strap being arranged with uniformly varying pitch and in the shape of a helix having end turns of substantially right cylindrical shape adiacent respectively to two spaced planes arranged at right angles to the longitudinal axis of said element, thereby to permit the formation of a uniform dense current sheet between said planes.

4. A preformed strap wound into a high frequency inductance coil having a helical winding, said strap consisting of a continuous sheet of conducting material having the shape oi one edge determined by Z=j(0) and having the shape of the other edge determined by Z=f(0+21r) where z is the ordinate and 0 the abscissa which equals the angle from the beginning of the winding to a given point on said strap, and where {(0) is determined by the desired variation in pitch of said coil, said strap further having two straight edges arranged parallel to the 0=0 axis, the length of said strap between said straight edges being determined by the desired number of turns in said winding and the diameter of said helical winding.

5. A preformed strap wound into a high frequency inductance coil having a helical winding with substantially right cylindrical end turns, said strap consisting of a continuous sheet of conducting material having one edge determined by 2:10) and having the other edge determined by Z=I(0+2r), where Z is the ordinate and e the abscissa which equals the angle from the beginning of the winding to a given point on said strap, and wher 1(0) is determined by the desired variation in pitch of said coil, said strap having two straight edges parallel'to the 0:0 axis. the length of said strap between said straight edges being determined by the desired number of turn in said winding and the diameter of said helical winding, said strap further including two substantially triangular end portions having their apices on said straight edge, each of said triangular end portions extending parallel to theZ=0 axisfor oneturnofsaidcoilandhavinganedge parallel to the 0=0 axis.

6. A preformed strap wound helically into a high frequency inductance coil having the shape of a right cylinder, said strap consisting of a continuous sheet of conducting material having two identical rectangular end portions, having a length equal to an integral number times the drcmnferenee of said cylinder and a width determined by the distance between the center of twoadiacentturnsofsaidcoihandhavingamain strap portion with parallel edges forming acute triangular end sections, said parallel edges each being integrally connected to one edge of a corstrapandarrangedinaiiathelixwithendturns flm loneofsaidrec ansularendportions,

said acute triangular end sections having the REFERENCES CITED acute angle determined by the desired a pitch The following references are of record in the angle of said coil.

file 01' this patent:

'7. A preformed strap helically wound into a tapered high frequency inductance coil having 5 STATES PATENTS a right cylindrical shape. said strap comprising Number Name Date a continuous sheet of conducting material having 508,620 Johnson et al, Nov. 14, 1893 a'main portion of substantial width bounded by 1,000,440 Reeves Aug. 15, 1911 two parabolae and terminated by'two straight 2,115,826 Norton May 3, 1938 edges spaced apart a distance determined by the 2,442,776 Newkirk June 8, 1948 desired number of windings of said coil, said strap further comprising two flared end portions each FOREIGN PATENTS having one edge parallel to said straight edges Number Country Date and a further edge extending at right angles 624.391 Germany 1936 thereto and positioned so asto provide right 15 cylindrical end turns 0! said coil.

WILLIAM F. SANDS. 

